Metabolic Engineering of the Yeast Schizosaccharomyces pombe Tolerant to Low pH for L-Lactic Acid Production

The recombinant strain based on the acidophilic yeast Schizosaccharomyces pombe with a cloned gene of heterologous lactate dehydrogenase (LDH) was used to optimize the biosynthesis of L-lactic acid. For this purpose, the effect of inactivation of pyruvate decarboxylase genes (PDC) on the synthesis of acetate, pyruvate, and ethanol (the main by-product in the synthesis of lactic acid) was studied. Using the wild S. pombe strain, we showed that the Δpdc3 and Δpdc4 deletions did not affect these indicators, while in the Δpdc1 mutant, ethanol biosynthesis was reduced and acetate biosynthesis was increased, and the Δpdc2 mutant accumulated pyruvate. The effect of deletions of the PDC1 and PDC2 genes on lactic acid biosynthesis was tested on a model S. pombe strain containing a heterologous LDH gene from Lactobacillus pentosus. It was shown that in strains with the inactivated PDC2 gene the accumulated pyruvate was poorly consumed for the biosynthesis of lactic acid even in the presence of two different recombinant lactate dehydrogenases; the introduction of the third gene of heterologous lactate dehydrogenase led to loss of viability of the strain. At the same time, in strains with the deleted PDC1 gene, the biosynthesis of lactic acid was enhanced with the introduction of additional LDH genes. The results obtained can be used in the design of industrial lactic acid producing strains.